Young adulthood is an important period in the development of regular cigarette smoking and nicotine dependence. Dramatic increases in both the prevalence and intensity of smoking occur after age 18. National data show that the prevalence of cigarette smoking is higher among young adults (aged 18-24) than among any other age group, and there is little evidence of a decline in these rates over the past several years. The primary goal of this proposed project is to continue to follow our established cohort of high risk adolescents through the period of young adulthood (approximately ages 19-25 for our cohort), with four annual assessments, and to examine the contributions of social and emotional contextual factors to the development of smoking patterns as they emerge from adolescence through young adulthood. We will examine how changes in social contexts (friendship networks, life transitions) may serve as markers for smoking change, and how specific behavioral risk factors (e.g., alcohol and substance use, depression, ADHD symptoms) may confer additional risk in developing nicotine dependence. In addition, we propose to examine, more in-depth, the phenomenon of nicotine dependence across the range of smoking levels, from light and infrequent smokers to more regular and heavier smokers, and how nicotine dependence is best assessed and conceptualized at different levels of smoking. This project will take advantage ofthe wealth of rich, longitudinal data already collected on this sample, with a unique opportunity to look specifically at mechanisms that might explain vulnerability to smoking progression and the development of dependence. We will be able to track changes in key variables and smoking from adolescence through young adulthood, and examine how both protective and risk vulnerabilities present during adolescence and emerging adulthood may play a role in predicting changes in smoking behavior. Understanding factors that influence the development of smoking patterns (both escalation and cessation) during the vulnerable period of adolescence to young adulthood is of critical importance for developing future interventions.